Touch technologies are commonly used as input devices for a variety of products. The usage of touch devices of various kinds is growing sharply due to the emergence of new mobile devices such as Personal Digital Assistants (PDA), tablet PCs and wireless Flat Panel Display (FPD) screen displays. These new devices are usually not connected to standard keyboards, mice or like input devices, which are deemed to limit their mobility. Instead there is a tendency to use touch sensitive digitizers of one kind or another. A stylus and/or fingertip may be used as a user input.
U.S. Pat. No. 7,372,455, entitled “Touch Detection for a Digitizer” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes a detector for detecting both a stylus and touches by fingers or like body parts on a digitizer sensor. The detector typically includes a digitizer sensor with a grid of sensing conductive lines, a source of oscillating electrical energy at a predetermined frequency, and detection circuitry for detecting a capacitive influence on the sensing conductive line when the oscillating electrical energy is applied, the capacitive influence being interpreted as a touch. The detector is capable of simultaneously detecting multiple finger touches.
US Patent Application Publication No. 20070062852, entitled “Apparatus for Object Information Detection and Methods of Using Same” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes a digitizer sensor and/or touchscreen sensitive to capacitive coupling and objects adapted to create a capacitive coupling with the sensor when a signal is input to the sensor. In some embodiments, the digitizer sensor includes a series of activated electrodes and passive electrodes. An AC signal, e.g. a pulsed AC signal, sequentially activates each of the activated electrodes. In response to each AC signal applied, a signal is transferred, by capacitive coupling, to each of the passive electrodes. The presence of a finger or an object typically alters the signal transferred to some of the passive electrodes. These signals are analyzed to determine the position/orientation/identification etc.
In some exemplary embodiments described in this reference, to speed up report rate, the active electrodes are divided into a number of groups wherein the active electrodes in each group are activated sequentially but the groups work simultaneously. This is accomplished by applying AC signals with non-mutually interfering (orthogonal) frequencies to each of the groups working simultaneously.
US Patent Application Publication Number US20060097991, entitled “Multipoint Touchscreen”, the contents of which is incorporated herein by reference, describes a touch screen having a transparent capacitive sensing medium to detect multiple touches or near touches that occur at the same time and at distinct locations. The touch screen includes a first set of lines that are electrified and a second set of lines crossing the first set that sense signals coupled by capacitive coupling at each of the nodes formed by the crossing lines. A multiplexer sequentially releases a signal to each of the lines of the first set. In response to each signal released, output is sampled from the second set of lines.